1. Field of the Invention
The present invention relates to a fluid control valve.
2. Description of Related Art
Hydraulic systems are commonly utilized in various vehicles, machines and equipment because of the mechanical advantage provided by hydraulic power. Most hydraulic systems contain a number of fluid control valves that control the actuation of the machine. The control valves typically switch states in response to an input command. The input command may be the rotation of a simple mechanical lever that moves an internal valve, or an electrical current which energizes a actuator and moves the internal valve. Actuator actuated valves can be coupled to a controller that can control the state of the valve and the actuation of the machine.
There are a number of different actuator actuated control valves. By way of example, there exist two-way valves, three-way valves, and four-way valves. A two-way valve includes two external ports and an internal valve which controls the flow of fluid through the valve. The internal valve is moved between two extreme positions. In one position the internal valve allows fluid communication between the ports. In the other position the internal valve prevents fluid communication between the ports. Two-way valves can provide an "on-off" switch for an hydraulic system.
Three-way valves contain a cylinder port, a supply port and a return port. Like the two-way valve, three-way valves contain an internal valve that moves between two extreme positions. In one position the internal valve couples the cylinder port to the supply port. In the other position the internal valve couples the cylinder port to the return port. Four-way valves have an additional second cylinder port and are constructed so that the first cylinder port is coupled to the supply port and the second cylinder port is coupled to the return port when the internal valve is in a first position. In the second valve position the first cylinder port is connected to the return port and the second cylinder port is connected to the supply port. By way of example, three-way control valves are used to control a spring return hydraulic piston. Four-way valves are used to control an hydraulic piston that does not have a spring return.
All three types of actuator actuated control valves have limitations on use within an hydraulic system. Two-way valves can only provide on and off functions. Three-way and four-way valves cannot be used to maintain a machine in an intermediate position. For example, when coupled to an hydraulic piston, three-way and four-way valves always couple the cylinder port(s) to either the supply or return lines. The piston is thus either fully extended or fully retracted. The system would require an additional two-way valve to maintain the piston at a location between the retracted and extended positions. It would be desirable to provide a actuator actuated control valve that has three positions.